///- --package .
:# combat_text static =
    :< testing

:< sm'_operators

:= digit_at (text : string) (at : i32) : option i32 =
    ? at >= sm'::length text ?> None |: convert::try_convert (sm'::substring at 1i32 text)

:~ ^ digits_from (text : string) (at : i32) (value : i32) : i32 * i32 =
    ?= digit_at text at ?|
    | Some d => digits_from text (at + 1i32) (value * 10i32 + d)
    | None => value, at

:= rest_from (at : i32) (text : string) : string = sm'::substring at (sm'::length text - at) text

:= starts_with_any (prefixes : list string) (text : string) : bool =
    listm::fold (\ found prefix => found || sm'::starts_with prefix text) !- prefixes

:== number_pattern = { before : string; ends : list string }

:= number_at (p : number_pattern) (found : i32) (text : string) : i32 =
    := start = found + sm'::length p::before
    := value, stop = digits_from text start 0i32
    ? stop > start && starts_with_any p::ends (rest_from stop text) ?> value |: -1i32

:~ ^ number_between (p : number_pattern) (text : string) : i32 =
    := found : i32 = sm'::index_of p::before text
    ? found < 0i32 ?> -1i32
    |:
        := n = number_at p found text
        ? n >= 0i32 ?> n |: number_between p (rest_from (found + 1i32) text)

:= hit_amount (text : string) : i32 =
    number_between { before = "loses "; ends = [ " hitpoints due to your"; " hitpoint due to your" ] } text

:= damage_taken (text : string) : i32 =
    number_between { before = "You lose "; ends = [ " hitpoints due to an attack"; " hitpoint due to an attack" ] } text

///> lua
:# hits_read_the_amount_the_monster_loses =
    := crit = "A rat loses 1 hitpoint due to your critical attack."
    (hit_amount "A troll loses 12 hitpoints due to your attack.", hit_amount crit) |> _assert_eq (12i32, 1i32)

///> lua
:# hits_skip_other_attackers_and_own_losses =
    := theirs = "A troll loses 12 hitpoints due to an attack by a cyclops."
    := mine = "You lose 30 hitpoints due to an attack by a troll."
    (hit_amount theirs, hit_amount mine) |> _assert_eq (-1i32, -1i32)

///> lua
:# damage_reads_the_amount_the_knight_loses =
    := rat = "You lose 1 hitpoint due to an attack by a rat."
    (damage_taken "You lose 30 hitpoints due to an attack by a troll.", damage_taken rat) |> _assert_eq (30i32, 1i32)

///> lua
:# damage_skips_monster_losses_and_mana =
    (damage_taken "A troll loses 12 hitpoints due to your attack.", damage_taken "You lose 5 mana.")
    |> _assert_eq (-1i32, -1i32)

///> lua
:# a_later_match_counts_when_an_earlier_one_does_not_fit =
    := p = { before = "loses "; ends = [ " hitpoints" ] }
    number_between p "it loses its way and loses 7 hitpoints" |> _assert_eq 7i32